4 lb. med. sized potatoes, scrubbed, not peeled
1/2 c. plus 2 tbsp. butter
1/3 c. finely chopped onion
1/2 c. finely chopped fresh parsley
4 lg. eggs, yolks & whites separated
1 1/2 c. milk
1 tsp. salt
1/4 tsp. ground nutmeg
1/4 tsp. pepper, preferably white pepper

Cook potatoes in a large pot of boiling water until tender, about 25 minutes. Meanwhile, melt the 1/2 cup butter in a small skillet over medium/low heat. Add onion and 1/4 cup parsley. Cook 6-8 minutes, stirring 3 or 4 times, until onion is translucent. Remove from heat.

Grease a shallow 3 quart baking dish (9 x 13 inch). Drain potatoes and when cool enough to handle, peel and cut in small chunks.

Meanwhile, beat egg yolks in a small bowl with a fork or whisk. Beat in the milk until well blended. Return potatoes to the pot and while gradually adding the milk-egg mixture, mash with a masher until smooth. Using a wooden spoon, beat in the onion mixture, salt, nutmeg and pepper.

In a clean dry bowl, beat egg whites until stiff peaks form. Stir 1 large spoonful into the potatoes to lighten them, then fold in remaining whites. Spoon mixture in prepared baking dish, mounding the top. Dot with the remaining 2 tablespoons butter. (If making ahead, bring to room temperature before baking.) Heat oven to 350 degrees, bake until nicely browned on top and heated through. Sprinkle with remaining chopped parsley.